1. Field of the Invention
This invention relates to a system for controlling a fuel pump for an internal combustion engine, and more particularly to a system for controlling an electric fuel pump for an internal combustion engine which uses a gasoline-alcohol blend fuel.
2. Description of the Prior Art
In an engine, more amount of fuel is required when the engine is full throttle opening than that required in idling state. And when the engine uses a gasoline-alcohol blend fuel, since the stoichiometric air-fuel ratio of gasoline is 14.7:1 while that of alcohol, e.g. methanol is 6.4:1, the amount of fuel required increases as the ratio of alcohol to gasoline in the fuel increases. Thus, when the engine adopts fuel system, an electric fuel injection pump for pumping fuel from a fuel tank must be controlled so as to satisfy the above.
Japanese Laid-open Patent Publication No. 3(1991)-61662 teaches a system of this type in which the flow rate of the electric fuel pump is determined on the basis of the alcohol concentration in the fuel so as to supply the optimum amount of fuel at all times without delay in delivery.
In such a conventional system, however, since the pump flow rate is continually controlled in proportion to the alcohol concentration, the circuitry for controlling the electric fuel pump is complex and costly.